Add WiFi reconnection retry logic to recover from unreliable WiFi

- Implement periodic WiFi reconnection attempts when stuck in AP mode
- Add WIFI_RECONNECT_INTERVAL_MS config (default 60s) for configurable retry frequency
- Prevent data loss by automatically attempting to switch back to STA mode
- Maintain AP mode for manual configuration if reconnection fails
- Track WiFi config and last reconnection attempt time in shared state
- Add wifi_try_reconnect_sta() and wifi_restore_ap_mode() helper functions
- Log reconnection attempts and results for debugging

include/config.h

@@ -63,6 +63,7 @@ constexpr uint8_t METER_BATCH_MAX_SAMPLES = 30;
 constexpr uint8_t BATCH_QUEUE_DEPTH = 10;
 constexpr BatchRetryPolicy BATCH_RETRY_POLICY = BatchRetryPolicy::Keep;
 constexpr uint32_t WATCHDOG_TIMEOUT_SEC = 120;
+constexpr uint32_t WIFI_RECONNECT_INTERVAL_MS = 60000;  // WiFi reconnection retry interval (1 minute)
 constexpr bool ENABLE_HA_DISCOVERY = true;
 #ifndef SERIAL_DEBUG_MODE_FLAG
 #define SERIAL_DEBUG_MODE_FLAG 0

include/wifi_manager.h

@@ -25,3 +25,5 @@ bool wifi_connect_sta(const WifiMqttConfig &config, uint32_t timeout_ms = 10000)
 void wifi_start_ap(const char *ap_ssid, const char *ap_pass);
 bool wifi_is_connected();
 String wifi_get_ssid();
+bool wifi_try_reconnect_sta(const WifiMqttConfig &config, uint32_t timeout_ms = 5000);
+void wifi_restore_ap_mode(const char *ap_ssid, const char *ap_pass);

src/app_context.h

@@ -4,6 +4,7 @@
 
 #include "config.h"
 #include "data_model.h"
+#include "wifi_manager.h"
 
 struct ReceiverSharedState {
   SenderStatus sender_statuses[NUM_SENDERS];
@@ -24,5 +25,11 @@ struct ReceiverSharedState {
   uint32_t receiver_last_error_ms;
   bool receiver_discovery_sent;
   bool ap_mode;
+  
+  // WiFi configuration and reconnection tracking
+  WifiMqttConfig wifi_config;
+  uint32_t last_wifi_reconnect_attempt_ms;
+  char ap_ssid[32];  // AP SSID for restoring AP mode if reconnection fails
+  char ap_password[32];  // AP password for restoring AP mode
 };
 

src/main.cpp

@@ -112,6 +112,11 @@ void setup() {
   display_set_sender_statuses(g_receiver_shared.sender_statuses, NUM_SENDERS);
 
   bool has_cfg = wifi_load_config(g_cfg);
+  
+  // Store WiFi config in shared state for later reconnection attempts
+  g_receiver_shared.wifi_config = g_cfg;
+  g_receiver_shared.last_wifi_reconnect_attempt_ms = 0;
+  
   if (has_cfg && wifi_connect_sta(g_cfg)) {
     g_receiver_shared.ap_mode = false;
     time_receiver_init(g_cfg.ntp_server_1.c_str(), g_cfg.ntp_server_2.c_str());
@@ -124,6 +129,13 @@ void setup() {
     char ap_ssid[32];
     snprintf(ap_ssid, sizeof(ap_ssid), "%s%04X", AP_SSID_PREFIX, g_short_id);
     wifi_start_ap(ap_ssid, AP_PASSWORD);
+    
+    // Store AP credentials in shared state for potential reconnection fallback
+    strncpy(g_receiver_shared.ap_ssid, ap_ssid, sizeof(g_receiver_shared.ap_ssid) - 1);
+    g_receiver_shared.ap_ssid[sizeof(g_receiver_shared.ap_ssid) - 1] = '\0';
+    strncpy(g_receiver_shared.ap_password, AP_PASSWORD, sizeof(g_receiver_shared.ap_password) - 1);
+    g_receiver_shared.ap_password[sizeof(g_receiver_shared.ap_password) - 1] = '\0';
+    
     if (g_cfg.ntp_server_1.isEmpty()) {
       g_cfg.ntp_server_1 = "pool.ntp.org";
     }

src/receiver_pipeline.cpp

@@ -198,7 +198,7 @@ static void write_u32_be(uint8_t *dst, uint32_t value) {
   dst[3] = static_cast<uint8_t>(value & 0xFF);
 }
 
-static uint32_t read_u32_be(const uint8_t *src) {
+uint32_t read_u32_be(const uint8_t *src) {
   return (static_cast<uint32_t>(src[0]) << 24) |
       (static_cast<uint32_t>(src[1]) << 16) |
       (static_cast<uint32_t>(src[2]) << 8) |
@@ -303,6 +303,51 @@ static bool process_batch_packet(const LoraPacket &pkt, BatchInput &out_batch, b
   return false;
 }
 
+// Helper function to attempt WiFi reconnection when stuck in AP mode
+// Retries WiFi connection periodically (configurable WIFI_RECONNECT_INTERVAL_MS) 
+// to recover from temporary WiFi outages
+static void try_wifi_reconnect_if_in_ap_mode() {
+  if (!g_ap_mode) {
+    // Already in STA mode, no need to reconnect
+    return;
+  }
+  
+  if (!g_shared || g_shared->wifi_config.ssid.length() == 0) {
+    // No valid WiFi config to reconnect with
+    return;
+  }
+  
+  uint32_t now_ms = millis();
+  
+  if (g_shared->last_wifi_reconnect_attempt_ms == 0 || 
+      now_ms - g_shared->last_wifi_reconnect_attempt_ms >= WIFI_RECONNECT_INTERVAL_MS) {
+    
+    // Update the last attempt time
+    g_shared->last_wifi_reconnect_attempt_ms = now_ms;
+    
+    if (SERIAL_DEBUG_MODE) {
+      serial_debug_printf("wifi_reconnect: attempting to reconnect from AP mode");
+    }
+    
+    // Try to reconnect with 10 second timeout
+    if (wifi_try_reconnect_sta(g_shared->wifi_config, 10000)) {
+      // Reconnection successful!
+      g_ap_mode = false;
+      if (SERIAL_DEBUG_MODE) {
+        serial_debug_printf("wifi_reconnect: reconnection successful, switching from AP to STA mode");
+      }
+    } else {
+      // Reconnection failed, restore AP mode to ensure web interface is available
+      if (g_shared->ap_ssid[0] != '\0') {
+        wifi_restore_ap_mode(g_shared->ap_ssid, g_shared->ap_password);
+        if (SERIAL_DEBUG_MODE) {
+          serial_debug_printf("wifi_reconnect: reconnection failed, restored AP mode");
+        }
+      }
+    }
+  }
+}
+
 static void receiver_loop() {
   watchdog_kick();
   LoraPacket pkt = {};
@@ -468,6 +513,9 @@ static void receiver_loop() {
   }
 
 receiver_loop_done:
+  // Try to reconnect to WiFi if stuck in AP mode due to unreliable WiFi
+  try_wifi_reconnect_if_in_ap_mode();
+  
   mqtt_loop();
   web_server_loop();
   if (ENABLE_HA_DISCOVERY && !g_receiver_discovery_sent) {

src/wifi_manager.cpp

@@ -143,3 +143,52 @@ bool wifi_is_connected() {
 String wifi_get_ssid() {
   return WiFi.SSID();
 }
+
+// Try to reconnect to WiFi with a shorter timeout (for periodic reconnection attempts)
+// Called when device is stuck in AP mode and we want to try switching back to STA
+bool wifi_try_reconnect_sta(const WifiMqttConfig &config, uint32_t timeout_ms) {
+  // Only attempt if not already connected and config is valid
+  if (WiFi.status() == WL_CONNECTED) {
+    return true;
+  }
+  
+  // Check if config is valid
+  if (config.ssid.length() == 0 || config.mqtt_host.length() == 0) {
+    return false;
+  }
+  
+  // Switch to STA mode and attempt connection with shorter timeout
+  WiFi.mode(WIFI_STA);
+  WiFi.begin(config.ssid.c_str(), config.password.c_str());
+  
+  uint32_t start = millis();
+  while (WiFi.status() != WL_CONNECTED && millis() - start < timeout_ms) {
+    delay(200);
+  }
+  
+  bool connected = WiFi.status() == WL_CONNECTED;
+  if (connected) {
+    esp_wifi_set_ps(WIFI_PS_MIN_MODEM);
+    if (SERIAL_DEBUG_MODE) {
+      Serial.printf("wifi_reconnect: success, connected to %s\n", config.ssid.c_str());
+    }
+  } else {
+    if (SERIAL_DEBUG_MODE) {
+      Serial.printf("wifi_reconnect: failed, remaining in STA mode\n");
+    }
+  }
+  
+  return connected;
+}
+
+// Helper function to restore AP mode when reconnection attempt has failed
+void wifi_restore_ap_mode(const char *ap_ssid, const char *ap_pass) {
+  if (WiFi.status() != WL_CONNECTED) {
+    // We're not connected to WiFi, restore AP mode
+    WiFi.mode(WIFI_AP);
+    WiFi.softAP(ap_ssid, ap_pass);
+    if (SERIAL_DEBUG_MODE) {
+      Serial.printf("wifi_restore_ap: AP mode restored\n");
+    }
+  }
+}